Last Updated: Nov 22, 2016     Views: 652

From Dr. Robert Brill, Research Scientist Emeritus:

The first point I would want to verify is whether or not the surface displays true "pitting".  "Pitting" implies the presence of minute depressions or holes in the surface, which is different from an accretion or buildup of charred foreign material.

Assuming that it is pitting, it doesn't seem to me that a chemical attack is behind it.  I don't believe there are chemical reactions that would take place between a hot, concentrated sugar solution and an inorganic glass cooktop.  But it is conceivable that if the syrup cooked down to a very concentrated solution that did not char completely, it could have formed hardened specks that might have become tightly bonded to the glass surface upon cooling.  It is then possible that if they were scraped away physically they might have chipped off tiny specks of the surface glass.  This would really be a physical effect, not a chemical change. (If the syrup became charred to some hardened carbonaceous residue, perhaps the same thing could have happened.)  However, this explanation is just speculation.

On the other hand, I have seen cases where solutions of gelatin were dried slowly in glass beakers (at room temperature) and actually fractured away thin chips of glass from the surface of the beakers.  Shrinkage of the tightly-adhering gelatin pulled glass away from the surface.  This was because the adhesive forces between the gelatin and glass were actually stronger than the cohesive forces holding the glass together. In fact, I believe that is one of the ways that diffusing glass windows were once made.  Gelatin solutions were dried out on plates of window glass.  Perhaps that could happen with a sugar solution as well, but it might be a little far-fetched.  

In any event, you might do well to direct your question to some manufacturer of glass or glass-ceramic cooktops.  They are the ones who could provide an authoritative answer.

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